Polypharmacy 2 Flashcards
5 common classes of medications that cause admissions
- NSAIDs - GI bleed, renal function
- Antiplatelets
- Anticoagulants
- Diuretics - AKI, electrolyte (low Na+), hypotension –> falls risk
- Antihypertensives
Where do medication errors commonly occur?
- Primary care
- Care homes
- Secondary care - least common - less patients to look after
Where in the journey do prescription errors occur?
- Prescription writing
- Dispensing
- Administration
- Transitions
What do clinical pharmacists do?
- Ward round participation
- Monitoring and reporting ADRs - via yellow book (post marketing surveillance)
- Therapeutic drug monitoring
- Prevention and monitoring drug interactions
- Patient counselling re medications
- Clinical research
What dose of morphine is suggested to then becomes useless for pain?
120mg per day - after this you begin getting more side effects and battle tolerance issues
How to prescribe liquid doses?
- Prescribe dosage - not mls
- As the liquids can come in different strengths
What is bioavailability?
- How much of the drug actual makes it to the blood stream to be able to then act on receptors
- It passes through GI tract and liver prior to this - will affect bioavailability depending on formulation (eg tablet, IV, subcut)
Morphine - oral to SC calculation
- Divide oral dose by 2
- Subcut = double strength of oral
Examples of medicines that should be prescribed by brand
- Anti-epileptics - varies between brands, affects bioavailability, if stable prescribe same again
- Insulin
What is medicine reconciliation
- Three C’s
- Collection - new medications, what they take and what they are prescribed, include OTC and herbal
- Checking - against reliable sources (at least 2)
- Communication
Sources we can use for medicines reconciliation
- Patient or carer
- Patients own medications (PODs) - supply on d/c
- Patients reminder charts - confirm with pt that they are new
- GP repeat prescriptions
- GP surgery/summary care record
- SystemOne - electronic patient record and recent outpatient letters
- Discharge letters or old drug charts if recently discharged after hospital admission
Targets of drugs - where can they act
- Mostly cellular (but not all eg antacid)
- Mostly proteins (either on cell surface or inside cells)
- Mostly receptors (agonists and antagonists)
- But can be ion channels, enzymes and transport proteins
- These are already there biologically, we then use drugs that act on them alongside natural substrate
What is pharmacodynamics?
What the drug does to the body - biochemical, physiological and therapeutic effects of drug
What is pharmacokinetics?
What the body does to the drug
* ADME
* Absorption - absorbed when reach blood, IV does not require (all others do)
* Distribution - movement of drug around body
* Metabolism - destruction of drug by chemical alteration (usually via liver)
* Excretion - removal of drug from body (eg kidneys or bile)
Elimination = metabolism + excretion
How can drug interactions work?
- Pharmacodynamic - Drug A alters action of Drug B - concentation of drug B in tissue fluid is unaltered but effect is altered
- Pharmacokinetic - drug A alters ADME of drug B - concentration of drug B that reaches site of action is altered
How do pharmacodynamics interactions work?
- One drug is affected by presence of another
- Compete for same drug target or act on same physiological system (eg lots of antihypertensives different classes = same system)
- Synergistic/additive (same effect/side effect) or antagonistic (oppose eachother)
Examples of synergistic effects
- Alcohol + diazepam - enhance GABA neurotransmission - different receptors
- Beta blocker and verapamil - work on same system, different receptors
- Potassium supplement + spironolactone - K+ sparing
Antagonistic interactions examples
- Antihypertensives and sympathomimetic decongestants (constricts blood vessels to reduce oedema and help drain nose)
- Anticoagulant and vitamin K
- Gliclazide and glucocorticoids (hypoglycaemia - stimulates pancreas to produce insulin, vs hyperglycaemia)
How do pharmacokinetic interactions work?
- Absorption - chelation/complexes (drug binds to drug or food = insoluble complexes not absorbed = therapeutic failure), changes of GI pH (acidic drugs absorb well in acid and same for alkaline), effects on GI motility, food effects (slower absorption if taken with meal and changes pH)
- Distribution - protein bound drugs displacing eachother (on albumin) = increased free drug levels in blood, mostly affects narrow TI drugs eg Warfarin, digoxin, phenytoin
- Metabolism - CYP450 inducers and inhibitors
What affects levels of albumin?
- Liver failure - reduced production
- Amino acids poor intake in diet - no ingredients to make albumin
CYP450 inhibitors
- Allopurinol (inhibitor) and Azathioprine
- Fluconazole and Warfarin
- Grapefruit juice and Ciclosporin
= increased blood conc of drug
CYP450 inducers
- Rifampicin (inducer) and phenytoin
- Carbamazepine and oral contraceptive
- Tobacco and theophylline
= reduced blood conc of drug
Drug and food interactions
- Food and absorption of abx
- Calcium in milk –> chelation
- Grapefruit juice being inhibitor
- Cranberry juice increasing effect of warfarin
- Tyramine (sympathomimetic) rich foods eg cheese, beer and wine metabolised by MAO - interact with MAOIs
- Vitamin K rich foods (greens) reducing effect of warfarin
- High protein foods and L-dopa (uses amino acid transporter to cross BBB - high protein meal will compete with L-dopa)
Resources to use for checking drug interactions
- BNF interaction checker
- Stockleys drug interactions
- HIV drug interaction checker
